Learning SMPS the hard way
by, 17th February 2012 at 20:32 (10538 Views)
SMPS is the toughest section in Power Electronics. With this subject, additional knowledge is required for choosing active and passive parts to be used in SMPS circuits. Special type of parts are often required as normal parts used in power electronics (low freq. application) may not be suitable all the times in case of SMPS.
When I started learning Power electronics, I put my emphasis on SMPS. But regarding SMPS, nothing was available here. So, I had to collect/gain everything piecemeal- knowledge, literature, active and passive parts, testing equipment etc. Main drawback was non availability of knowledge. In my country, in no engineering university, SMPS is taught in detail. So, teachers are not readily available.
So, my father chalked out a deliberate and detailed plan for my learning of SMPS:
Detail Plan for learning SMPS at home
Step 1 – Collecting knowledge by collecting required books from abroad.
Step2 – Surfing internet for SMPS related knowledge.
Step3 – Collecting test equipments.
Step4 – Collecting minimum required parts.
Step5 – Learning and collecting different types of Ferrite Cores and knowing in detail regarding winding of Ferrite Cores in different Topologies.
Step6 – Learning PCB making software and making PCBs.
Step7 – Collecting and practicing SMPS in hardware and in simulation software.
Step8 – Testing the test circuits on verroboard.
Step9 – Assembling the circuits on PCB and testing in detail.
Step10 – Finding out drawbacks and making necessary corrections.
Accordingly, I collected lots of books related to SMPS.
The first book with which I started to learn Power electronics/SMPS was “Power Electronics Demystified” by Chandra Shekhar Roy and the book was collected from Kolkata, India. That is a very good book for new starters.
Some of the important books collected by me are as follows:
a. Power Supply Cookbook ------ Marty Brown.
b. Practical Switching Power Supply Design------- Marty Brown.
c. Power Sources and Supplies ----- Marty Brown editor.
d. Switching Power Supply Design ------- Abraham I Pressmen.
e. High Frequency Switching Power Supplies-Theory and Design –George Chryssis.
f. Demystifying Switching Power Supplies ---- Raymond A. Mack,Jr.
g. Practical Design of Power Supplies ----- Ron Lenk.
h. Regulated Power Supplies ----- Irving M. Gottleb.
i. Switching Converters Medium and High-power --- Dorin O Neacsu.
j. Principles and Elements of Power electronics ---- Barry w William
k. Switch mode Power Converters Design & Analysis --- Keng C Wu.
l. Switch mode Power Supply Handbook --- Keith H. Billings.
m. Power Electronics Handbook – Industrial Electronics Series --- Edited by Timothy L. Skvarinina of Purdue University.
n. Power Mosfets –Theory and Application -Duncan A Grant and John Gower.
o. Digital Power Electronics and Applications—Fang Lin Luo, Hong Ye, Muhammad Rashid.
p. Switching Power Supplies A to Z --- Sanjaya Maniktala
Most of the test equipment including Oscilloscope were collected locally. For initial test circuits, good quality parts were collected. But one thing was very irritating. Whenever I made a test circuit, capacitors occasionally leaked and were destroyed. With a lot of effort, I found that in high frequency circuits, normal capacitors cannot be used, rather low ESR type capacitors are to be used. How would I find out which capacitors are of low ESR? So, an ESR meter was collected from abroad and with that meter, low ESR capacitors were collected from local market. Same thing happened with normal diodes also and I came to know ultimately that for high frequency SMPS circuits, ultrafast or schottky diodes need to be used, not the normal diodes.
Next problem was with Ferrite core. In local market, required ferrite cores were not available. After a lot of searching, few ETD39 type ferrite cores made by Chinese manufacturers were found, which were available as spares for flyback transformers used in Chinese non-branded television sets available in local market. I collected some, unwound and split into 2 parts, and rewound the bobbin by hand to use in test circuits. Initially I faced problem as those cores had big air gap as they were meant for flyback topology and could not be used in a optimum way in other topologies, where air gap is not required. Problem was also there regarding use of required size of wire in different frequencies and those problems could be overcome by gaining knowledge regarding the phenomenon of “Skin Effect” in high frequency circuits. With the passage of time, I could gather knowledge regarding different type of cores – like EE, EC, EI, ETD, Toroidal – and their application in different topology of SMPS, winding speciality and could collect some from China with the help of local suppliers.
To collect the required active and passive parts for SMPS circuits, one has to have detailed knowledge regarding those and I had to work really hard to gather appropriate knowledge regarding those. For that hundreds of hours had to be spent through reading books, surfing net, going through forum contents, reading datasheets etc. After getting bare minimum knowledge required, it became easier to collect required parts for test circuits from home and abroad. One of my aunts lives in USA and I have collected lots of parts from USA through her.
I could not manage any useful software for SMPS hardware simulation. But for making PCB, I learned and used PROTEUS ARES software. Since I require only few pieces for each test circuit, professional PCB makers were usually unwilling to make my PCB and hence I was in a real dilemma. So, from internet, I learnt how to make PCB and started to make in my house with Ferric Chloride, Sticker paper, Laser printer and Iron.
Almost everything was sorted out but one crucial thing remained. Professional transformer winders of the local market were not acquainted with Ferrite Core winding and hence I personally had to wind by hand all the transformers for different Topologies with different sizes of wire and also with Litz wire (self-made) in the initial test circuits.
For sorting out different problems in different stages of early test circuits, in the first 3 years, I made almost 300 circuits. Though almost all of those circuits were unsuccessful for different drawbacks, I learnt valuable practical lessons from those failures. By correcting those drawbacks and learning lessons from those, I am now confident and by applying the gathered knowledge of SMPS with microcontroller, I started building some successful circuits of practical value.
I love reading SMPS books like reading novels. Making SMPS circuits is like playing games to me.
Learning SMPS is really difficult but one can learn it with passion, patience, hard work, dedication and relentless effort.
If any beginner in SMPS finds anything useful for his pursuit of learning, my effort of narrating my difficult journey in SMPS world will be worth the trouble.